Flowed film

ABSTRACT

310,540. Celluloid Corporation, (Assignees of Stevens, J. H., and Walsh. J. F.). April 27, 1928, [Convention date]. Cellulose esters; cellulose ethers; apparatus for making films.-Films or sheets are prepared from solutions or dopes of cellulose derivatives, such as cellulose nitrates, acetates, or propionates or methyl or ethyl celluloses, bv extruding them or causing them to flow at elevated temperature into an atmosphere which has an augmented pressure. The use of these higher temperatures enables smaller amounts of solvent, to be employed and results in more rapid setting and drying and consequently in an increased rate of production of the sheets or films. Any suitable volatile solvents such as acetone, ethyl acetate, ethyl or methyl alcohol, or higher boiling point solvents or mixtures thereof may be used. When volatile solvents are employed alone or with higher boiling point solvents, the solutions can, for example, be used at about 130‹ F. whilst when higher boiling point solvents are used alone, the solutions can be used, for example, at about 180‹ F. but the temperature naturally depends upon the boiling points of the particular solvents employed and the pressure conditions existing. The temperatures may be maintained somewhat below the boiling points of the solvents. The solution is kept at the chosen temperature at least up to the point where it is caused to flow or be extruded on to the forming surface or even during the remaining steps of the process. The augmented pressure results in a uniform product and prevents the formation of bubbles in the film or sheet. This pressure should be exerted not only during extrusion but also whilst the sheet or film is on the forming surface, for example a wheel, belt, or table. Thus, the atmosphere of the room can be maintained at a pressure nearly equal to that exerted on the solution in the feeding apparatus but not so high that it interferes with extrusion. This increased pressure also results in a reduction in the amount of solvent required to give a flowable solution. Any suitable apparatus may be employed but it is preferable to force a thin stream of solution from a hopper so that it makes a direct fall on to the forming surface, the distance of travel between the point where the film solution leaves the hopper and the forming surface being short, prefer. ably so that the wheel or belt exerts a drag or pull, which assists the extrusion of the solution. The process is suitable, for example, for the production of films or sheets for cinematographic and other photographic purposes. In an example, a solution of cellulose acetate with mono-methylxylene-sulphonamide dibutyl tartrnte, or diethyl phthalate as plastifier in acetone and dioxane is heated to 130‹ F. and extruded on to a film wheel in an atmosphere having pressure of 30 1b. per square inch above atmospheric pressure. In another example, cellulose acetate with ethyl lactate and a plastifier is dissolved in dioxane. The solution is heated to 180‹ F. and extruded as in the previous example.

Patented June 19, 1934 UNITED STATES FLOWED'FILM" John H. Stevens, South Orange, and James F. Walsh, East Orange, N. J., assignors to' Celluloid Corporation, a corporation of New Jersey No Drawing. Application April 27, 1928,

I Serial No. 273,424

9 Claims. (CI. 1857) This invention relatesto the manufacture of films and sheets from cellulose derivatives, whereby improved films are obtained at a greater rate of production and at a lower cost.

An object of this invention is to produce flowed films or sheets from solutions of cellulose derivatives. Anotherobject of this invention is to devise a process for the production of flowed films and sheets wherein the amount of solvent required for producing the solution of the cellulose derivative is considerably lessened. Another object of this invention is to produce flowed films and sheets which shall be free-from bubbles and other similar defects. Other objects and advantages will appear hereinafter in the specification and claims. 7

The films to which our invention'relates are usually made by spreading solutions of cellulosic derivatives on the moving surface of a wheel and, after suitable exposure to evaporating influences, stripping the set and dried product in practically endless form, subject, of course, to further drying if such be found necessary. 7 Such sheets or films have long found extensive employ in cinematograph applications and hand cameras;

' but our object is to extend their use to the entire commercial field, which we are enabled to do as a result of the lower production cost made possible by'our invention. i 1 7 The usual sheet of celluloid or otherplastic made by pressing and planing costs less than a flowed sheet, and for that reason has greatly restricted the use of flowed films and sheets despite their superior qualities. Such superiority, as is well known, liesin the cleanliness and permanent surface as well as the greater strength of sheets deposited from solution. Sheets-or films produced in this manner are not subject to the accidents of roll and press manipulation, neither are they subject to contamination due to factory dirt or careless handling.

One of the causes of high cost in a flowed sheet is the large proportion of solvent necessary to maintain a fiowable condition. Not only is there a resultant wastage of solvent in spite of recovery methods, but the necessity of evaporating such ity of the mass is increased, and 'asa result a smaller amount or proportionof solvent (vola tile solvent) maybe successfully used in making up the solution from which the films, sheets, etc e t be de- V V I 5.0

In addition to lowering the proportion of sole vent necessary tobe used, our invention alsoerr-- pedites to a marked degree the setting and drying of the films, sheets, etc. This is due to thefact that there is less solvent to be removedand also 6 to the fact that the solution is at elevated tem; perature. All thesefactors result inlargenproductionper unit of time or machine than -was heretofore possible.

Accordingto our invention the dope or solu- 70, tion of cellulose derivative is heated to a tem: perature somewhat below the boiling pointof-the solvent or solvents present. The solutionis maintained at this elevated temperature throughoutthe remaining steps of the process or v at least up to the; point where the solutionis spread or extruded upon the film or sheet forming surface, which may be a wheel, belt, plane surface etc. In other words, this elevated; tem: perature is maintained upon the solution during its travel throughout all parts of the storage and feed apparatus. 1 r r In order to insure a uniform'product andto prevent the formation of bubbles in the film, or sheet because of the elevated temperatures em ployed, we have found it desirablet maintain the heated (warm) ,solutionunder pressure. Such pressure shouldbe maintained not; onlypn-the solution during process but also after thesame has-been deposited upon the wheel,-belt, etc. This can be accomplished by maintaining the room where the film is formed under, a pressure nearly equal to that imposed upon the solution in the feedingapparatus, but not high enough. to inter fere with adjustment to the demands ofjextrusion. After meeting this necessity, the room pressure should be as high as possible, due regard being given to the comfort and safety of the operators. The use of pressure on the solution has the unusual advantage of facilitating the 190 flow of the dope or solution from the so called hopper to the belt or wheel. It also cuts down the amount of solvent required in the process to form a fiowable solution.

The construction of the usual wheel apparatus, with its attendant hopper and dope supply system being well known, it is unnecessary to describe the apparatus required for the operations. A suitable adjustment or variation of the film forming system described in U. S. Patent 573,928 issued llO to one of us will accomplish our object. We prefer to force a band or thin str am of dope from such hopper in a way to make a direct fall upon the wheel surface and thus minimize the evaporation of solvent before deposit.

To facilitate this rapid formation of a film or sheet deposit, we find that it is desirable to so arrange the wheel, belt or other surface that there is only a short distance between it and the point at which the dope or solution emerges from the hopper. Excellent results are obtained by having the wheel or belt so close to the point of emergence, that the wheel or belt will act as a drag or pull to withdraw the dope or solution.

With the belt or wheel operating at constant speed this will result in a uniform film or sheet.

In this process the well known volatile solvents solvents alone are used, the dope or solution can be maintained at a temperature of about 180 F. These figures are, of course, illustrative as the temperature which can be used will depend upon the boiling points of the particular solvents em ployed under the pressure conditions existing in the system.

- This invention is applicable to the manufacture of flowed films or sheets from solutions or'dopes The term cellulose embraces within its scope cellulose esters, such as nitro cellulose, cellulose acetate, cellulose pro pionate as well as cellulose ethers'such as ethyl V cellulose, methyl cellulose, etc. i

' Any solvent or solvents capable of dissolving the cellulose derivative "are also embraced within the scope of this invention. The term film as used in the description and claims is to be construed as including within its scope sheets as well as -films while the term flowing used" in the claims is to be construed as including extrusion.

Having described our invention-what we claim and desire to secure by Letters Patent is:

1. In a process of making films from solution's of substitution derivatives of cellulosecontaining a relatively small proportion of solvent by flowing, the step of maintaining the solution above room temperature and under superatmospheric pressure. r

2. ma process of making" films from cellulose ester solutions containing a relatively small proportion of solvent by flowing, the step of maintaining the cellulose ester solution under superatmospheric pressure and at approximately 130 F.

3. In a process of making films from cellulose acetate solutions containing a relatively small proportion of solvent by flowing, the step of maintaining the cellulose acetate solution under superatmospheric pressure and at approximately 4. Process of producing 1 flowed films which comprises adding to a substitution derivative of cellulose a solvent therefor, the amount of solvent added being insufficient to form an easily flowable solution at room temperatures, heating, under superatrnospheric pressure, the solution of the cellulose derivative thus formed and extruding the heated solution onto a film wheel.

5.. Process of producing flowed films which comprises adding to a cellulose ester a solvent therefor, theamount of solvent added being insufficient to form an easily fiowable solution at room temperature, heating, under superatmospheric pressure, the solution of the cellulose ester thus formed and'extruding the heated solution onto a film wheel. g i

6. Process of producing flowed films which comprises adding to a cellulose acetate-a solvent therefor, the amount of solvent added being insuflicient to form an easily flowablesolution at room temperatures, heating, under. 'superatmospheric pressure, the solution of the cellulose acetate thus formed. and extruding the heated S0111?- tion onto a film wheel.

7.Process of producing flowed films which comprises adding to cellulose acetate a solvent therefor, the amount of solvent added being insufiicient to form an. easily flowable' solution at room temperature, heating, under superatmose pheric pressure, the solution of the cellulose ace? tate thus formed and extruding the heated solution onto'a film wheel. whose surface is exposed to a pressure approaching. that imposed on the heated solution in process. I

8. Process of producing flowed films which com- I prises adding to a substitution derivative of cellulose a'solvent therefor, the amount of solvent added being insufficient to form an easily flowable solution at ordinary temperatures, heating the solution of the cellulosederivative thus formed to approximately 130 F. and extruding the'heate ed solution onto'a film wheel. c

9. Process of producing flowed films-which com-'- prises. adding to cellulose acetate asolvent there- 'ioo 

